i put a bigger cam in my truck (1994 chevy k1500 5.7 nv3500 3.73 gears) and was gonna do the ultmate tbi mods and was thinking about putting a aqustable fuel pressure regulator on it but found some 14psi regulator springs for $20 and was wondering if they were worth buying or to stay away from them

 

Does your scan tool show that the ECM is having any problem fueling the engine now? What is your fuel pressure at WFO-maximum RPM?

$20 for a regulator spring is NUTS--but it saves you from going to a well-equipped hardware store and sticking your hand in the bins of compression springs to select one for yourself. Depending on how well-stocked your local hardware store is, paying $20 for a $4 spring may still be better than buying an adjustable regulator.

 

i have no idea what the pressure is now and when we hooked up the big snap-on scan tool at school i think it was a lil rich but i did have a vacuum leak that's now fixed ill pull it in the shop tomorrow and see what it says

 

A 100% stock engine needs 13 psi of fuel pressure to run correctly at WOT. With airflow enhancing modifications it needs more than 14 psi. The engine can be showing BLM values lower than 128 at idle and light throttle, indicating rich, but can still be running too lean under throttle.

 

Why do you say this? My K1500 currently has 11.5 psi, seems to run just fine at any throttle position including WFO.

For that matter, it ran fine at 10--10.5 psi even though it needed to have the screwy O2 sensor that was setting false codes replaced. (It would set false "lean" code, but actually ran just fine.)

My block learn numbers don't show rich-command to make up for low-fuel-pressure induced leanness.

 

The reason I say this is experimentation with about 20 of these engines so far. Every last one of them has responded well to 13-13.5 psi fuel pressure and the timing set at 6-8* BTDC.

I put a wideband on a stock long block 1995 350 TBI 4 dr Yukon recently that was a DOG despite a recent crate engine, headers, exhaust, 46mm throttle body and complete tune-up. It would fall off leaner than 13:1 at any rpm greater than 2,500 rpm and WFO. By the 3,500 rpm it had fallen to 15:1 air/fuel ratio and we aborted the run. A fuel pressure check had the pressure at only 10 psi. The fuel pressure regulator had about the lowest cup setting I have ever seen for a factory regulator. Modified the factory regulator to be adjustable and re-adjusted to get 13.5 psi. WFO now had an air fuel ratio running from about 12.2:1 at 2,500 to 13:1 at 4,500 rpm. Bumped the timing from -2* to 4* and made a timed acceleration run. Then bumped the timing to 8* and made another run, saw some burst knock during the run on the datalog. Went back to 6* and made another run. No knock and the quickest 0-60 yet. At 13.5 it was a little richer than I like to see, so brought it down to 13.25. At 13.25 the midrange was about 12.5:1 and peak HP about 13.2:1. With zero changes to the engine itself or the chip the engine felt like it picked up about 30 HP and matching torque throughout the RPM range. It was running a little hot at this point. Replaced the failed fan clutch and the 195*F thermostat with a 180*F thermostat. Was then able to run 8* timing for the quickest 0-60 run.

 

I guess I have another project...

 

 

Sorry it took a while to show yall but my teacher wouldent let us go to the shop but it looks like it's running lean

 

Open loop, 120 degrees F. coolant temp.

Your data is meaningless until it's fully warmed-up and in closed-loop. And then, you'll need to DRIVE or DYNO the vehicle to replicate the heavy-throttle use you're concerned about.

 

Ok I'll hopefully get to pull it back in tomorrow and drive around with it and see what it says

 

Thea were taken right after each other the bottom one was taken first

 

Who cares what's happening at idle and off-idle. That's not when the heavy demand for fuel occurs.

Show me a screen shot of what's happening when your throttle pedal is on the carpet, the RPM is 5000+, in high gear.

THEN we'll know if that engine is rich or lean.